Radio alarm system



Aug. 16, 1932. DURKEE 1,872,257

RADIO ALARM SYSTEM Filed Dec. 5, 1950 2 Sheets-Sheet 1 *HIHIIEIHP IN VEN TOR.

JAM/D D. QM/Mew,

BY 6 Q g g ATTORNEY Aug, 1 1932. DURKEE I 1,872,257

RADIO ALARM SYSTEM Filed Dec. 5, 1930 2 Sheets-Sheet 2 INVENTOR. wwvwo D, BM (Kw,

, I Q C; ATTOR EY.,

Patented Aug. 16, 1932 UNITED STATES PATENT OFFICE RADIO ALARM SYSTEM Application filed December 5, 1930. Serial No. 500,391.

My invention relates broadly to a radio transmission and reception distress signal system and more particularly to a circuit ar rangement for a transmitter and receiver by which a warning signal may betransmitted andcaused to actuate an indicator automatically at a receiver regardless of other signals occurring simultaneously on the distress signal frequency.

One of the objects of my invention is to provide a radio alarm system for transmitting a distress signal effectively through radio traffic for positively actuating a warning signal at receivers within the range of the transmitter.

Another object of my invention is to provide circuit arrangements for transmission and receiving apparatus for the positive transmission of a distress signal for automatically operating an indicator at a receiver where the signal is distinctive in character and recognizable through regular radio traffic or static for automatically actuating an alarm at receivers within the range of the transmitter.

A further object of my invention is to provide a selective system for the transmission and reception of distress systems for the automatic operation of a warning at receivers within the range of the transmitter operating 3 independently of interference and other signals occurring simultaneously with the transmission of the distress signal.

Other and further objects of my invention reside in the circuit arrangements for the 5 transmitting and receiving apparatus as set forth more fully in the specification hereinafterv following by reference to the accompanying drawings, in which:

Figure 1 shows the circuits of my invention applied to the signal transmitter; and Fig. 2 shows the circuit of my invention as arranged in each receiving station for auto.- matically responding to a distress signal.

The alarm system of my invention is simple in operation, construction and mainte nance, and will reject allunwanted impulses and accept the signal intendedto operate the device. The system is certain in operation and emits a distinctive easily recognized signal through regular radio traflic.

In Fig. 1, I have shown the transmitter of my alarm system as a simple quenched spark gap type radio transmitter, where 1 is the antenna, 2 the secondary of the oscillation transformer, the ground, 3 the primary of the oscillation transformer, 4 the quenched spark gap, 5 the primary condenser, 6 the power transformer, 7 the transmitting key and 8 the motor-generator; 9 is a source of direct current for energizing coils 11 of the tuning fork 12, 10 a single pole switch, 13 and 14 are vibrating contacts of tuning fork 12; 19 and 20 stationary contacts of tuning fork 12; 15 a source of direct current for energizing coil 16 of the relay 21; 17 isthe contact on armature 22 of relay 21; 18 is the stationary contact of relay 21. When the motor-generator is started and the radio transmitter is adjusted for operation in the usual manner, the switch 10 is closed 7 and tuning fork 12 given an initial impulse by striking. The fork will continue to vibrate at its natural period, making and breaking contact 13 and 20, which supply energy to coils 11 and 23 from battery 9, magnetizing cores 26 and 27 periodically at the natural frequency of the tuning fork 12, thus supplying the driving energy to maintain fork 12 in continuous vibration. Contacts 19 and 14 are made and broken at the period of vibration of the fork 12, completing the circuit from battery 15 through coil 16 operating armature 22 which makes and breaks contacts 17 and 18 which are across key 7 of the transmitter thus keying the radio transmitter at the natural frequency of the fork l2. Tuning fork 12 may be tuned to any frequency within the audio range, however a frequency of about thirty cycles, will produce an easily recognized signal of a very distinctive quality which, when used as a dis.- tress signal for ships will attract immediate attention as well as being easily recognized and recorded through interfering strays and other signals on the usual wave lengths employed for regular radio traffic.

Fig. 2 shows the recorder of my invention connected to a simple regenerative receiver and two stages of audio frequency amplification where 30 indicates the receiving antenna,

32 the primary of the receiving transformer, 33 the ground connection, 34 the secondary of the receiving transformer, 35 the variable tuning condenser, 36 the grid leak and condenser, 37' the grids of the detector and amplifier tubes, 38 the filaments of the detector and amplifier tubes, and 39 the plates of the detector and amplifier tubes. The tickler coil of the receiver is shown at 40. The primary windings of the first and second audio frequency transformers have been designated at 41. The secondary of the first andsecond audio frequency transformers have been indicated by reference character 42. The plate batteries for the detector and audio amplifier tubes have been shown at 43. The filament lighting rheostats for the detector, amplifier, rectifier and relay tubes are shown .at 44. The filament heating batteries for the detector, amplifier, rectifier and relay tubes are shown at 45. The primary of the rectifier input transformer is shown at 46. The

V secondary of the rectifier input transformer isindicated at 47. The plate of the rectifier tube is shown at 48. The filament of the rectifier tube is designated at 49. The rectifier filter condenser is shown at 50. A relay tube 51 is connected across the rectifier tube and includes filament 52, grid 53 and plate 54. Reference character 55 indicates the impulse coil of the relay 56 connected in series With the relay charging condenser 57. Reference character 58 designates the relay charging resistance and 59 the relay charging battery. 60 designates the north pole of relay magnet 56, 61 the south pole of relay magnet 56, 62 the north pole and 63 the south pole of relay magnet" 64. The vibrating armature of the relay 56 is indicated at 65, 66 indicates the core of the impulse coil 55, 67 and 68 are the stationary contacts of the relay. 69 is the vibrating contact of the armature 65. 70 the source of current for driving coil 71 of the tuning fork 72. 73 is the coil of the driving coil 71. 74 is the stationary contact and 7 5- the moving contact of the fork 72. 76 is a signal lamp and 77 a source of current for lighting lamp 76.

The operation of a regenerative receiver and of a two stage audio frequency amplifier is already well known. The operation of the relay and control circuit and rectifierhas been fully explained in my copending application Serial No. 316,511, filed November 1, 1928. The operation of the relay shown in Fig. 2 is described as follows: The permanent magnet 56 exerts a continual attracting on armature by completing its magnetic path through armature 65 from north pole 60 to south pole 61. This attraction is equally counterbalanced by a like attraction of the magnet 64 which completes its magnetic path from north pole 62 through armature 65 to south pole 63. Poles 60 and 62 being of a like nature expend no magnetic energy through core 66 of impulse coil 55. However when there is a flow of current through coil 55 in one direction, the end 60 of core 66 becomes north, adding to the attraction of pole 60 on armature 65 and becomes south at the end 62 repulsing armature 65 at the latter end.

The operation of the recording system is as follows: The filament batteries 45 are connected to filaments 38, 49 and 52 and the receiver adjusted to receive the desired frequency in the usual-manner. If the incoming signal is being continuously keyed by the tuning fork 12 at the transmitter and associated apparatus shown in Fig. 1, the signal after being received and amplified by the receiver and amplifier shown in Fig. 2, it is put into the primary '46 of the input transformer, and induced into secondary 47 of the input transformer and rectified by the rectifier circuit including electrodes 48-49 in the usual manner. The energy is impressed on the relay tube grid 53 and relay tube filament 52 in the form of direct current impulses. The condenser 50 tends to smooth out the direct current impulses; Each direct current impulse on the relay grid 53 being of negative character will block the flow of current from plate 54 to filament 52 allowing condenser 57 to charge through therelay coil 55 causing the armature 65 to move towards contact .68 thereby completing the circuit from battery through coil 71 and contact 69 to contact 68. The flow of current through coil 71 will momentarily magnetize' core 73, attracting the ends of the tuning fork 72 inward- An impulse of current in an. opposite direction will produce the effects set forth above in the opposite sense. At the-end of each direct current impulse on grid 53 and filament52, the electronic path from plate 54 to filament 52' is restored and condenser 57 will be discharged by battery '59 through coil 55 and resistance 58. If armature 65 has not already resumed its normal position between contact 68 and 67, the discharging of condenser 57 through coil 55 by thebattery 59 will attract armature 65 in the direction of contact 67 thus breaking the circuit from battery 70 through coil 71 at contacts 69 and 68. The core 73 no longer attracting the fork 72 allows thefork 72 to start vibrating.

If the fork 12 at the transmitter of Fig. 1, has a natural period of vibration of 25 cycles and the fork 72 of Fig. 2 has the same natural period of vibration, the above described process will be repeated 25 times per second and the vibration of the fork 72 shown in Fig. 2, will in a very short time, approximately one second or more, build up to a point where contact 7 5 makes and breaks with contact 74 completing the circuit from battery 77 causing lamp 76 to become lighted.

The armature 65 may be, mechanically tuned to respond to a particular frequency such as 25 cycles thus increasing the selectivity of the system. An adjustable mechanical tuning system may be provided so that'the period of the armature 'may be changed as desired to render the system selective to a particular transmission frequency.

Inasmuch as static and other unwanted signals do not recur over any considerable period of time, that is for the most part substantially longer than one second of time at the precise frequency of 25 cycles per second, these signals will not build the vibrations of fork 72 up to a point where light is sustained to vision in lamp 7 6 by the making and breaking of contacts 7 5 and 74. Lamp 76 may be replaced by some audible alarm such as a bell or buzzer where desired to further attract the attention of the operator at the receiver.

At a frequency of 25 cycles it is possible without great refinement of machine work to build a simple mechanical fork or reed which will kee a fairly constant frequency and it further 1s possible to adjust and regulate the magnitude of the amplitude of the vibrating element to build up to the desired response in the desired time interval.

At frequencies higher than 25 cycles, particularly with frequencies of 100 cycles or more, the natural amplitudes of the forks or reeds decrease and the frequency is also somewhat more difiicult to maintain, tuned to the degree to provide a precalculated amplitude response. With the decrease in natural amplitudes the contacts to bring a response of the alarm must be positioned nearer the vibrating element and the adjustment therefore more closely regulated. There is a possibility on account of this of shock excitation of the vibrating reed or fork and therefore of false signals.

By keeping the tuned system in the vicinity of 25 cycles the system has been found to respond excellently and faithfully and to give no stray or false signals. Since the frequency is low, a longer signal may be used as the distress signal than would ordinarily be chosen since the amplitude of the vibrating element may be built up over a longer period of time. In a high frequency the building up is fairly rapid in time and therefore long signals do not aid materially while with low frequencies the building up of the amplitude of the vibrating system may be spread over a considerable time, in fact a time longer than the duration of the ordinary code signal in traffic or the ordinary static interference. With a 25 cycle frequency a note of one second in length can be usefully employed and the vibratory system so regulated that it will not respond to signals of much less duration.

The circuit employed in the present system also aids to prevent the operation of the system on false signals. This feature of the circuit is brought about more particularly by the combination of the rectifier tube and relay tube 51. The rectifier tube serves practically to cut off the flow of current one way in the secondary 47 of the transformer. As shown in Fig. 2 when the lower side of the secondary 47 becomes positive, curr t 111 e flow from anode 4:8 to cathode 4:9 and as a result the grid 53 becomes more negatively biased. When the potential is reversed in the secondary 47 nothing happens, for the grid 53 does not become more positively charged with respect to the filament 52. Since the grid normally is at the potential of the filament, a plate current corresponding to the zero bias and plate voltage will flow. This may be approximately f {so liamperesfor the ordinary receiving tubes used in radio work. The plate current never rises higher than this. However, it may be cut off to zero either in the operation of the circuit by the signal or in the operation by operated by this because it requires about twenty-five signals inabo-ut one second and therefore when the interfering code or static comes in, the circuit may be blocked if the interference is powerful enough so that not even the warning signal will come through. However, the instant that the powerful interference ceases, the charge accumulated on the condenser 50 is relieved by the resistance across it if it has become charged which is unlikely on account of its size, and the circuit is again in normal operative state. The blocking of the circuit is never so long but that the longer distress signal comes through without difiiculty.

The distinctive character of the signal emitted by the alarm circuit of my invention enables a warning to be given which will insure the reception of the distress signal at receivers within the range of the transmitter emitting the distress signal.

While I have shown my invention applied to a spark transmitter, it will be understood that the alarm circuit of my invention may be employed to control the modulation of any type of transmitter, and I do not intend by the disclosure herein to limit my invention to the particular transmitter or receiving ap- What I claim as new and desire to secure by Letters Patent of the United States is as follows: r r

1. In a distress signal transmission and receiving system, a receiving circuit including mechanical means adapted to respond only to a low audio frequency signal, an alarm, a local energizing circuit having contacts closed by the operation of said mechanical means for operating said alarm,.and means for adjusting the position of said contacts to obtain the desired magnitude of amplitude of said mechanical means before said alarm will be energized.

2. In a distress signal transmission and receiving system, a receiving circuit including means adapted to build up a response of a given magnitude only to an audio frequency signal of approximately twenty-five cycles per second persistent continuously for a time greater than approximately one second, an alarm, and means controlled by said first means for operating said alarm when the said given magnitude has been attained.

3. In a distress signal transmission and receiving system, a receiving circuit including mechanical means adapted tobuild up a response of a given magnitude only to an audio frequency signal of approximately twentyfive cycles per second persistent continuously for a time greater than approximately one second, an alarm, and means controlled by said first means for operating said alarm when the said given magnitude has been attained.

at. In a distress signal transmission and receiving system, a receiving circuit including a mechanically tuned means adapted to build up'a response of a given magnitude only to a definite low audio frequency signal persistent continuously for a timegr-eater than approximately one second, an alarm, a local energizing circuit including contacts operated by said first means for operating said alarm and means to adjust the position. of said contacts whereby the alarm may be operated when the said given magnitude has been attained. V

5. In a distress signal transmission and receiving system, a receiving circuit including a relay operating tube having cathode, anode and grid elements, and a normal cathode anode current, means operative through an applied signal only to apply a more negative charge of said grid, means operative when the applied signal is removed for allowing said normal cathode-anode current to be reestablished, and an alarm operating means responsive only to a definite periodic decrease of said current.

6. In a distress signal transmission and receiving system, a receiving circuit including a relay operating tube having cathode, anode and grid elements and a normal cathode an ode current, means operative through an apradio wave.

plied signal only to apply a more negative charge to said grid, means operative when the applied signal is removed for allowing said normal cathode anode current to be reestablished and an alarm operating means comprising an electro-responsive mechanically tuned device responsive only to a definite periodic decrease of said current corresponding in period to the tuning of said tuned device.

7 In a distress signal transmission and receivingsystem for receiving a radio wave interrupted at alow audio frequency in the neighborhood of 25 cycles per second, a receivingcircuit including a rectifier tube for producing unidirectional impulses of current from the received wave impulses, mechanical vibratory means positioned directly in the output of said receiving circuit, said vibratory means having a polarized reed relay including an operating coil, a condenser in series operative relation to the operating coil and means in theoutput of said receiving circuit for producinga charge and discharge of said condenser through said coil first in one direction and then in the reverse direction for producing alternating current of the desired low audio frequency from the interrupted whereof I aflix my signature.

In testimony JAMES D. DURKEE. 

